1. Field of the Invention
The present invention relates to a vehicle steering apparatus capable of a smooth and small turn at a large steering angle and a parallel movement in a substantially lateral direction, and to a vehicle provided with the same.
2. Description of the Prior Art
In general, four wheels are required to have a turning center for a smooth turn of a four-wheeled vehicle. For this purpose, conventional steering mechanisms have employed steering link mechanisms provided with, for instance, knuckle arms and tie rods.
In this steering link mechanism, as shown in FIG. 3, tie rods 01 are rotatably connected at tie rod ends 01a to ends of knuckle arms 02. The opposite ends of knuckle arms 02 are connected to king pins 03 of right and left wheels, respectively. Each tie rod 01 in this steering mechanism is adapted to be moved laterally or in right and left directions by a steering torque applied from a steering wheel through, for instance, a rack-and-pinion gear, a worm gear or a hydraulic cylinder so as to turn the knuckle arm 02. In this manner, the right and left wheels are laterally steered.
In many conventional automobiles, as shown in FIG. 4, each front wheel 04 is supported by a suspension 05 of a strut type. In this arrangement, a king pin offset is formed between the front wheel 04 and the suspension 05, and the steering force required on the steering wheel depends on the amount of this king pin offset. Thus, a larger amount of the king pin offset causes a larger steering force required on the steering wheel.
However, in such steering mechanism, the tie rod 01 and the knuckle arm 02 may be rectilinearly aligned with each other, as shown in FIG. 3, in which case further steering operation for the wheels can not be carried out. This condition is a limit of an allowable wheel steering operation and the limit for steering angle .alpha. is generally of about 45 degrees. The limit in the wheel steering will restrict the steering operation for the small turn.
Futher, if the apparatus were designed to set the steering angle .alpha. of the wheels to a value exceeding the limit, e.g., 90 degrees, a problem would be created in that the wheels could not be driven by driving power from a driving source provided on a vehicle body at the steering angle .alpha. of 90 degrees.
In view of the above, the applicant has already filed the Japanese Patent Application No. 63-165498 for a steering mechanism and a vehicle provided with the same, in which the above problems are eliminated.
In the steering mechanism and the vehicle provided with the same disclosed in this patent application, steering angle of the steering wheel is mechanically transmitted to the wheels through a link mechanism in such a manner that the steering angle is increased by a multiplying gear set provided on the vehicle frame, and driving motors are individually associated with the respective wheels.
Usage of the multiplying gear set for each wheel enables steering over 90 degrees as well as rotational driving by the driving motors at the steering angle of 90 degrees.
The steering mechanism thus employing the multiplying gear set may be used for each of the front and rear wheels, in which case the front wheels as well as the rear wheels may be steered at 90 degrees, which enables a small turn and a parallel movement in a lateral direction.
This steering mechanism, however, is adapted to transmit the steering force, which is increased by the multiplying gear sets on the vehicle body, through the torque link to each wheel to be steered. Therefore, rattling may be caused at three points in the torque link, which may cause an unstable steering operation of the wheel. Further, since the velocity increasing gear is formed of a pair of external gear wheels, the knuckle arm may interfere with a wheel or a tire if a sufficient distance is not left therebetween.
On the other hand, a conventional suspension structure shown in FIG. 4 is provided with a knuckle arm 06 of the steering mechanism, which is formed integrally with the strut 05a. In this structure, since an angle .beta. and the position of the king pin axis are determined by upper and lower supporting points of the knuckle arm 06, the amount of the king pin offset can not be sufficiently reduced. Therefore, there is created a problem in that the steering force required on the steering wheel is relatively large.
Accordingly, it is an object of the invention to provide a vehicle steering apparatus, overcoming the above-noted problems, in which the rattling in the steering link mechanism and the resulting unstable steering movement of the wheels can be prevented, and thus the running stability can be improved.
It is another object of the invention to provide a vehicle steering device in which steering force can be reduced.
It is still another object of the invention to provide a vehicle in which a small turn and a parallel movement can be smoothly and surely achieved even at a large steering angle.